Glass Distortion Measurement

Many video cameras including inexpensive webcams do a decent job of picking up near IR.

Some of it will depend on the frequency of the laser, but most of the commonly available IR diode lasers should be no problem to pick up.

Is the glass relatively transparent to IR?

There may also be slight variations in the distortion for IR as opposed to visible light, but I doubt it will be large enough to be of concern if you are staying in near IR.

Check the transmissivity (or whatever the word is) of the glass at the wavelength you intend to use before spending any money on hardware.

Good point - Thanks

Keep in mind that the index of refraction for IR is typically lower than for visible light, so the amount of distortion you measure may not match the optical distortion (it would be less than for visible light).

If you need to use a laser, use a green laser; that would be the best in term of matching what the eye would see.

Great information. I have tried the green laser and it works well. I was concerned that I would require more power to get a visible reading through the tinted glass and end up introducing a liability in production with the more powerful laser.

Very good - thank you so much.

Infrared viewer cards are available...

https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=infrared+viewer+card&tbm=shop

Strain in glass can be accurately measured by use of a polarimeter. It is an accurate quantitative method that may be useful for your application.

Objectionable distortion? Tempering adds distortion, Laminating adds distortion, Glazing pressures add distortion and then there are environmental causes like temperature changes and wind load. These are all combined effects that are present after installation of the window.

First you have to define what objectionable distortion is. Are the individual panes of tempered glass being inspected to any distortion standard after tempering?

You say it's tinted glass. Is it tinted or Low-E? Most window glass is Low-E in order to meet insulation standards. Metals in the Low-E would have some effect on any test using IR. Even pick up any problems in how it's applied as a distortion.

Objectionable distortion is my choice of description. Best I can define is the same effect as .008 depression with in a 10 inch diameter. I agree with all of your suggestions of cause. My purpose was to address the accumulation of those variables in a viewers perspective. Even when that perception is an acute angle. I do not presume I will be effective in addressing cause and having it prevented given the low occurrence rate. Approx. 0.25%. Good point about the Low-E re. IR.

Thanks

I agree; you requested information on measuring strain in glass, not in identification of its root causes. Strain can be measured using photo-elastic methods described by " Strain Measurements and Stress Analysis" by A.Khan and X.Wang.

Are you suggesting measurement of Strain would detect distortion?

I'm doing more than suggesting it, strain is the same is distortion. They are synonyms.

In the quench process in tempering glass it does leave circular distortion. The problem may be aligning two such distortion over top of each other. Creating the effects of a lens.

In tempering large runs of single sized glass these quench marks are usually always in identical positions on the glass. You can see this on large glass buildings.

Thanks for the feedback. I'm leaning more towards observing reflective distortion.

0.5%? As much as that? It's obviously not Japanese glass.

Correct - not Japanese glass. US made tempered in Columbia SA. the .5% is rejectable but not necessarily rejected by the end user. Cut that in half for distortion that is noticed, and another half for lites that people will formally complain about i.e. requesting replacement.

I'm now using a bright light focused to cover just the lite perimeter set about 4M from the lite and the lite set at 45-30 degrees. The refraction possibly caused by the shift in density and the optics in the distorted area shows up clearly on a white board.

light/lite? You managed it once with "a bright light" - what went wrong?

I apologize. I'm just getting used to the fenestration vernacular myself. What I meant was Light = Light and Lite = glass. Bright light = 200 lumens @6500K or there about.

Not sure what went wrong but can say feel reasonably sure I'm moving towards a solution to weed out he weak components at pre glazing that result in objectionable glass window distortion.

That is good news.